A special type of hydraulic fluid designed specifically for brakes Brake fluid transfers the motion of a driver stepping on a brake pedal directly to operate a brake caliper or wheel cylinder
The brake system uses a special kind of alcohol-based hydraulic fluid The fluid is "hydroscopic," which means it tends to absorb moisture over time (never leave a can of brake fluid open for this reason) Moisture lowers the boiling point of the fluid and causes internal corrosion in the brake system That's why the fluid should be replaced when brake repairs are made or every couple of years, whichever comes first The best kind of brake fluid is silicone-based It won't absorb moisture and doesn't require periodic replacement -- but it costs several times as much as ordinary brake fluid